GB1309059A - Hydraulic boost mechanism - Google Patents

Abstract

1309059 Brake boosters BENDIX CORP 11 Jan 1972 [28 Jan 1971] 1287/72 Heading F2F An hydraulic boost mechanism comprises a housing 16 having a bore 18, a piston reciprocable in the bore and dividing the latter into two chambers 32, 34 located at respective ends of the piston, inlet and outlet ports 20, 78 and a working port 26 in communication with the bore, and a valve 58 slidably positioned within the piston for controlling fluid flow between the ports and the chambers; the piston comprises two telescopically related members 35, 36 each of which is circumferentially recessed for maintaining continuous communication with an associated port to obtain maximum piston stroke for a given bore length. As shown, a piston 35 is telescopically slidable in a sleeve 36 slidable in the bore 18 of the housing 16, the piston actuating a brake master cylinder through a force transmitting rod 60. The device is connected to an engine driven pump via the inlet port 20 and via the working port 26 to a steering gear 14 communicating with the pump via a return line 28. In operation, with the pump 12 operating, hydraulic fluid circulates freely through port 20, recesses 40 and 52 respectively in the sleeve and piston, passage 53 the opening between the valve seat 72 and valve ball 68, passage 55, recess 42 in the piston, passage 44, recess 38 in the sleeve, port 26, steering gear 14 and to the pump. Movement of the member 74 to operate the booster firstly seats the valve member 75 on the ball 68 to cut off chamber 34 from port 78 and then connects that chamber to the inlet 20, further movement of the members 74, 75 seating the ball on the seat 72, the chamber 34 then being exposed to the full main pressure source except that which is by-passed by the passages 71 to provide for operation of the gear 14. The piston 35 is thereby moved to the left to act on the rod 60 and activate the master cylinder. Release of the member 74 allows return of the piston and valve 58 to the initial positions as shown. In the event of insufficient supply of fluid from the pump, the deficiency is sensed by flow sensitive device 92 which actuates an electric pump 86 connected to an inlet port 89 communicating with recesses 40, 52, passage 53, the opening between the valve seat 72 and ball 68, passage 55, recess 42, passage 44, recess 38 and port 26. This subsidiary source from the pump 86 acts through conduit 102 and passage 100 on the valve 96 to shut off communication with the port 26 and the rest of the hydraulic system including the gear 14, circulation of fluid within the piston and valve occuring through the shunt path 106 connecting the recesses 38 and 40 of the sleeve 36. Whether the main or subsidiary source of fluid is producing movement of the piston means 30, comprising the piston 35 and sleeve 36, application of pressure fluid to the chamber 34 advances the piston into the sleeve until the land 48 of the piston contacts the sleeve end 50, communication between the ports 20 and 26 being maintained.